Transducer and mounting for mechanical delay lines



1111112151 J a. BRQMBAUGH 3,189,686

TRANSDUCER AND MOUNTING FOR MECHANICAL DELAY LINES Filed Aug. 18, 1961SOURCE OF T E S\QNRLS INVENTOR Jon-4m B. Enzomsnueu ATTORNEYS UnitedStates Patent 3,189,686 TRANSDUCER AND MOUNTING FGR MECHANICAL DELAYLINES John B. Bromhaugh, Cincinnati, Ohio, assignor to D. H. BaldwinCompany, a corporation of Ohio Filed Aug. 18, 1961, Ser. No. 132,329 1sClaims. (U. 1791) The present invention relates generally toelectro-mechanical and to mechanico-electrical transduction in delaylines and reverberators, and more particularly to devices and'methodsfor coupling transducers to long wire mechanical delay lines, formechanically mounting the delay lines, for effective generation oftransverse mechanical waves on the delay lines and for effectivetranslation of the mechanical waves into electrical signals.

Long wires, preferably in the form of helical springs, are useful forgenerating reverberation effects, in music,- approximating acousticreverberations produced by the acoustic properties of large reverberantspaces. Such reverberation generators may be operative at sonicfrequencies or at ultra-sonic frequencies. In the former case the outputof an electrical musical instrument, such as an electronic organ, or ofa phonograph, tape recorder, or other source of electrical signalsrepresentative of music, is directly coupled to a driverelectro-mechanical transducer which provides mechanical vibrations inthe wire. A mechanico-electrical transducer is coupled to the wire at apoint remote from the driver for translating the vibrations intoelectrical signals suitable for subsequent electro-acoustictransduction. The structural arrangement of the system is such thatmultiple reflections occur at the transducers or at other selectedpoints along the wire.

In the alternative, electrical signals representative of music aremodulated on an ultrasonic carrier, or are heterodyned to fall in theultrasonic range, and the converted signals are employed to generatereverberative mechanical vibrations on a wire at one point of the wire.The vibrations are transduced to electrical signals at a remote pointalong the wire and the electrical signals, with reverberative effectsnow added, are derived from the carrier by frequency conversion.

The present invention concerns itself primarily with ultrasonicreverberation systems, in terms of a preferred application. Theinvention, however, finds further application to sonic reverberators, tomechanical filters, to mechanical delay lines, and the like.

Briefly describing a preferred embodiment of the invention, elongatedtransducers are cemented to a wire delay line, ends of the transducerscoinciding with the ends of the wire, and the transducers being one halfwave length long or less at all operating frequencies and bondedlengthwise along the length of the wire. One of the transducers operatesas a driver and one as a pick-up, but

in other respects they may be duplicates. Preferably the transducersoperate in the longitudinally vibrating mode, causing and sensingtransverse vibrations in the wire. Leads for the transducers andsuspensions for the wire are secured to velocity nodes along thetransducer and the wire, to avoid reflections and attenuation. Thesuspensions may be fabricated of organic material, rather than metallicmaterial.

Since the transducers vibrate longitudinally, either piezo-electric ormagneto-strictive transducers can be employed. The latter type possesseslow impedance and therefore is particularly suitable in conjunction withtransistor circuitry.

The transducer mounting system of the present inven tion is particularlyapplicable to ultrasonic reverberator systems because for such systemsthe transducers can be small and the velocity nodes separated by slightdistances.

Wire delay lines have resonances, due to reflections from the ends ofthe wire. The fact that the transducers are bonded to the wirealong-their length implies that they are mechanically integral with thewire, or are seen as a thickening thereof by the mechanical wave motionof the wire. The transducers do not appreciably disturb the resonancecharacteristics of the wire, because of the mode of association of thetransducers and the Wire and high efiiciency of transduction exists.

It is, accordingly, a primary object of the present invention to providea novel reverberator.

It is another object of the invention to provide a novelelectromechanical transducer system.

A further object of the invention resides in the provision of a novelmechanico-electrical transducer system.

A further object of the invention resides in the provision of atransducer capable of transducing mechanical waves to and from anelongated wire, having resonance characteristics due to its length,without materially affecting these resonance characteristics.

It is another object of the invention to provide a transducer having twoleads, for generating and sensing traveling Wave mechanical vibrations,wherein the leads are located at velocity nodes of the vibrations.

Another object of the invention is to provide a mounting for anelongated mechanically vibrating rod or wire, the mounting consisting ofone or more suspensions secured to the rod or wire at velocity nodes.

A further object of the invention is to provide an organic fiber (nylon)suspension for wire having vibrations traveling along its length, thesuspension contacting the wire only at a velocity node of thevibrations.

It is still a further object of the invention to provide a transducerfor transverse vibrations in a wire, the transducer operating in thelongitudinal vibrational mode and being not longer than one half wavelength at the operating frequency.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein:

FIGURE 1 is a view in plan of a piezo-electric transducer secured to awire and including wire leads for the transducer and a mounting elementfor the wire.

FIGURE 2 is a schematized view of a reverberation system according tothe invention, incorporating the structure of FIGURE 1.

Refer-ring now to the accompanying drawings, FIGURE 1 illustrates ingeneral fashion a mode of coupling a transducer 1 to an elongatedelement 2, such as a long wire, for the purpose of inducing mechanicalvibrations therein, and sensing such vibrations. The transducer may beelectro-mechanical or mechanico-electrical. Further, the transducer ispreferably pieZo-electrlc (but magneto-strictive transducers can also beemployed). Its length is M12 or less at its operating frequency. Itsmode of vibration is preferably longitudinal, although piezo-electrictransducers operating in the bending or fiexural mode are usable. Leads3 may be secured, in the case of a piezo-electric transducer, one to thetransducer at a point occupied by a velocity node and the other to theWire 3, also at a velocity node. Thereby, the leads do not adverselyaffect the operation of the system. The transducer 1 may be bonded alongits entire length to the wire 2 by means of a conductive epoxy resin orby soldering. It is then found that the epoxy provides better acousticaland mechanical properties than the solder, for reasons which are notwell understood.

if the transducer 1 is considered as a driver operating in the bendingor flexing mode, transverse waves are directly generated in the wire 2and are coupled into the wire by the bond between the wire and thetransducer. If the transducer 1 is operating as a pick-up, in thebending or flexing mode, transverse vibrations in the wire 2. arecommunicated to the transducer via the epoxy bond and generate voltagetherein.

It is found that superior results can be attained by employing atransducer operating in the longitudinal mode. Moreover, it is this modeof operation which enables magnetostrictive transducers to be employed,having low impedance, with consequent advantages in conjunction withtransistor circuitry. The transducer, operating as a driver, and thewire 2, bonded to the transducer along the entire length of thetransducer, provide a structure in which one element, transducer 1,expands lengthwise, in response to a signal, while the other, the wire2, does not expand lengthwise. The result is a bending action. Theaction is similar to that which takes place in a bi-metallic thermostat.Operation of the transducer in the longitudinal extension mode providesmore output than transducers operating in the fiexural mode, for a giventransducer material, by a factor of about 10-13 db, in systems whichhave been tested. When operating as a driver, the transducer is requiredto'be M2 or less in length, at the operating wave-length, in order thatall points of the transducer shall contribute to bending of the wire inthe same direction, since the bending constitutes or generates atransverse mechanical vibration which travels down the wire. Were thetransducer longer than M2 there would exist points along the Wire,Within the bonded area, which were attempting to vibrate in phaseopposition to the motion of the transducer, thus reducing the efliciencyof transduction.

Alternatively, when the transducer operates as a pickup the transversemechanical vibrations of the wires elongate the transducer in bendingit. Maximum output occurs, per unit length of transducer, if thetransducer is M2 or less in length at the operating frequency.

The mechanical thickness of the wire at the bond aifects the mechanicalimpedance of the wire 4 and thus the coupling to the driver. Thisimpedance is high, for usual zWire sizes, in comparison with theimpedance of the driver, so that system resonance is not stronglyaffected by the properties of the driver, constituting an importantadvantage of the system. System resonance is very broad and occurs Wherethe driver is a half Wave length long of the Wave in the combination ofdriver and wire. One velocity node will occur along the driver, or atits end when it is half a wave length long. A lead wire 3 is attached atthis point, so that the lead wire will have minimum damping efifect andtherefore generate minimum reduction of reverberation time. The wireitself, being bonded to an electrode of the transducers employed, formsa common ground for the driver and pick-up transducers. A groundconnection to the wire may be soldered to the wire at a node, to avoiddamping.

In a practical reverberator, the wire takes the form of a helical spring4, but solely to conserve space for a given length of wire. Vibrationdoes not take place in the spring, as a spring, but in the wire as awire. The turns of wire are non-contiguous, to avoid frictional damping,The spring 4 requires mounting, in any practical reverberator. It isentirely feasible to effect mounting at one end of the spring, butgreater mechanical stability is achieved by mounting the spring at bothends and permitting the spring to hang free. In order to minimizeeffects of the mountings on reverberation time, the mountings are in theform of loops of organic fiber 5 e.g. nylon, from which the spring issuspended at velocity nodes closest to the transducers. It has beenfound that use of organic fiber suspensions, rather than metallicsuspensions, provides superior acoustic effects, although reasons forthis are not certainly known. Nevertheless, metallic wire suspensionsare operative. It is believed that the effect may be due to highacoustic damping in thefi-ber, i.e. the organic fiber does not respondto impact. The wire itself is (fl bent, as at d, to establish thevelocity nodal point on the wire, and to assure that the suspension willoccur at such a point. If metallic suspensions are employed they may besoldered to the wire, in which case the bend 6 is no longer necessary. ai

In an effective reverberator it is essential that repeated reflectionsoccur from both ends of the spring, i.e. that the vibrations travel backand forth along the spring and are reflected from the pick-up end of thespring to the driver end, and back to the pick-up end. A considerablenumber of two-way traverses may take place. This implies that thetransducers do not unduly interfere with reflections from the ends ofthe wires.

Construction of a transducer according to the present invention providesmaximum reverberation time, and minimum damping due to transd cers,leads and suspensions, the major part of the damping occurring in thespring itself. By proper choice of spring material, wire size and wirediameter attenuation along the wire of the spring can be minimized. Thissubject has been dealt With in a copending application, Serial No.102,443, Bissonette et al., filed April 12, 1961, now Patent No.3,136,853, and entitled Music Enhancing System, the con-tents of whichare incorporated herein by reference.

In a practical application of the present invention to a supersonicreverberator, of the types described more in detail in theabove-mentioned application for US. patent, a carrier generator 1dprovides carrier at about 20 kc. to a modulator 11. The carrier ismodulated, preferably in amplitude, by the tonal input of an electricalmusic source 12, such as an electronic organ, a phonograph, a radio, orthe like. The modulator 11 may be any one of the types referred to inthe above-mentioned application for US. patent, or any other type knownto the art which is capable of translating a band of frequencies in theaudio range to a band of frequencies displaced into the'supersonicrange.

The output of modulator Ill is applied to a transducer 1a, preferably aceramic piezo-eiectric transducer vibrating in the longitudinal mode.The transducer 1a is cemented by means of conductive epoxy resin to aflat formed at the end of a wire transducer. A lead 3a is secured to oneelectrode of the transducer, at a velocity node, and a ground connectionis provided on the Wire itself, either at the velocity node nearest tothe transducer 1a, or to the end of the wire. A bend 6a is formed in thewire, at a velocity node, and the wire is supported from the bend 6a bymeans of a nylon loop 50, secured to a rigid member 13.

At the remote end of the spring, the structure and arrangement is amirror image of those at the driver end, numerals of referenceemploying, however, the subscript b. The pick-up lb is connected to asuitable demodulator, 15, for detecting the modulation present in themodulated carrier traveling along the delay line 4, and the detectedoutput is suitably amplified by amplifier 16 and radiated acousticallyby loudspeaker 17.

The delay line 4 is designed to have adequate delay time to producereverberative effects, due to repeated refiections along the delay line.The transducers 1a and 1b do not introduce material attenuations, andreflections effectively occur from the ends of the wire, which are ofzero acoustic impedances. Therefore, reflection is substantiallycomplete. However, there is sufficient internal attenuation in the delayline to accomplish the requisite decay of signal, as a function of time,to simulate true acoustic reverberation as it ocurs in a reverberativespace.

A supersonic reverberator employing a long wire delay line possessesvery many resonances, which are desirable in enhancing music. The systemof the present invention, and the various features thereof, have beenfound to leave all resonances in the delay line substantiallyunaffected. Neither the presence of the transducers, nor a the leads toand from the transducer, nor the suspensions,

introduce damping or reflections. All reflections occur from the ends ofthe wires, which represent zero acoustic impedances, so that reflectionsare essentially total. Moreover, the many operational features of theinvention are accomplished by means of a structure which serves toprotect the transducers, which are quite small and fragile, from shock,impact, and mechanical strains, deriving from any source or cause.

What we claim is:

1. A reverberation system for electrically generated musical tones,comprising a source of electrical tone signals, a modulator, asupersonic carrier generator coupled .to said modulator, said modulatorgenerating a modulated carrier including said tone signals superposed onsaid carrier, a reverberator having a driver, a long mechanical delayline and a pick-up, a demodulator coupled to said pick-up, saiddemodulator being responsive to said modulated carrier to recover saidtone signals, and means for acoustically transducing said tone signals,said driver and said pick-up each including an elongated transducer,said delay line including a long wire, and means providing a direct bondbet-ween said transducers and said wire along at least a major part ofthe transducers, said transducers being adapted to vibrate along thebond.

2. The combination according to claim 1 wherein said transducers arepiezo-electric transducers including electrodes, an electrode of each ofsaid transducers being Ibonded along its entire length to said wire,whereby said wire constitutes a common ground for said transducers.

3. The combination according to claim 2 wherein said transducers aremounted end to end with said wire and are not greater than one half wavelength long along the wire.

4. The combination according to claim 3 wherein wire leads for saidtransducers are secured to nodal points of said transducers and of saidwire.

5. The combination according to claim 4 wherein said wire forms ahelical coil, and wherein said helical coil is suspended, at least someof said suspensions being located at nodal points along said wire.

6. A reverberatory system for introducing into music reverberatoryeffects simulating those of a large enclosure, said system including aflexible wire delay line, said delay line having free ends to providesubstantially zero acoustic impedance and therefore maximum wavereflections from said ends, a first transducer for inducing transverseacoustic vibrations of said flexible wire, a second transducerresponsive to said transverse acoustic vibrations for generatingelectrical signals, means providing a direct bond between saidtransducers and said wire along at least a major part of thetransducers, said transducers being adapted to vibrate along the bond,each of said transducers .being elongated and having two free ends, afree end of each transducer substantially coinciding with a free end ofsaid wire and the remaining ends of said transducers coinciding withpoints along said wire substantially displaced from the free ends ofsaid Wires.

7. The combination according to claim 6 wherein said means providing adirect bond is conductive epoxy resin.

8. The combination according to claim 7 wherein is provided a supersoniccarrier generator, modulating means responsive to said music formodulating said carrier,

means connecting said modulating means to said first transducer indriving relation thereto, said last means comprising a lead connected tosaid transducer at a velocity node of its vibrations.

9. The combination according to claim 8 wherein is further provided alead connecting said modulating means to said wire at a velocity node ofthe vibrations of said wire.

14 The combination according to claim 9 wherein are provided suspensionsfor said wire located at velocity nodes of the vibrations of said wire.

ii. The combination according to claim 10 wherein said wire is providedwith bends at said last mentioned velocity nodes, said suspensions beingorganic fibers suspending said bends, said wire hanging free betweensaid bends.

v12. The combination according to claim 11 wherein said bends arelocated between said transducers along said wires.

15. The combination according to claim 12 wherein said suspensions arelocated at the nodes located nearest to said transducers.

1d. The combination according to claim 13 wherein said transducers areeach not greater than one half wave length long at the Wave length ofsaid carrier along said wire.

15. The combination according to claim 14 wherein said transducers arearranged and adapted respectively to vibrate longitudinally in thedirection of the length of said wire in response to a driving signalwhereby said first transducer vibrates said wire in the transverse modeand said second transducer responds to said transverse vibrations.

16. The combination according to claim 15 wherein the lengths of saidwire adjacent the ends of said wire include flats and wherein saidtransducers are ceramic piezo-electric transducers bonded to said fiats.

References Cited by the Examiner UNITED STATES PATENTS 1,852,795 4/32Wegel 333-30 2,318,417 5/43 Phelps 179-1 2,375,004 5/ 45 Knowles 179-12,421,424 6/ 47 Kreuzer 1791 2,767,336 10/56 Arenberg 3333O 2,967,4471/61 Hanert 179-1 2,982,819 5/61 Meinema et al. 179-1 3,012,211 12/61Mason 333-30 3,025,479 3/62 Wolfshill 33330 3,041,556 6/62 Meitzler333-30 3,051,915 8/62 Hoover et al. 333-30 3,064,241 11/62 Schneider333-30 X 3,070,761 12/62 Rankin 33330 3,136,853 6/64 Bissonette et al1791 FOREIGN PATENTS 512,067 1/53 Italy.

ROBERT H. ROSE, Primary Examiner.

THOMAS B. HA'BECKER, WILLIAM C. COOPER,

Examiners.

1. A REVERBERATION SYSTEM FOR ELECTRICALLY GENERATED MUSICAL TONES,COMPRISING A SOURCE OF ELECTRICAL TONE SIGNALS, A MODULATOR, ASUPERSONIC CARRIER GENERATOR COUPLED TO SAID MODULATING, SAID MODULATORGENERATING A MODULATED CARRIER INCLUDING SAID TONE SIGNALS SUPERPOSED ONSAID CARRIER, A REVERBERATOR HAVING A DRIVER, A LONG MECHANICAL DELAYLINE AND A PICK-UP, A DEMODULATOR COUPLED TO SAID PICK-UP, SAIDDEMODULATOR BEING RESPONSIVE TO SAID MODULATED CARRIER TO RECOVER SAIDTONE SIGNALS, AND MEANS FOR ACOUSTICALLY TRANSDUCING SAID TONE SIGNALS,SAID DRIVER AND SAID PICK-UP EACH INCLUDING AN ELONGATED TRANSDUCER,SAID DELAY LINE INCLUDING A LONG WIRE, AND MEANS PROVIDING A DIRECT BONDBETWEEN SAID TRANSDUCERS AND SAID WIRE ALONG AT LEAST A MAJOR PART OFTHE TRANSDUCERS, SAID TRANSDUCERS BEING ADAPTED TO VIBRATE ALONG THEBOND.